Ilan Epstein

Arginine is one of the twenty common amino acids that make up proteins, and it is unique for its positively charged side chain. Once a protein has been synthesized, arginine inside it can be modified by adding or changing groups of atoms, leading to changes in the protein’s structure and overall function. One of these modifications is the addition of a carbon bonded to three hydrogens, which is called a methyl group. Arginine within proteins can be modified into three types of methylarginine by enzymes called protein arginine methyltransferases (PRMTs), and the modification changes the amino acid’s charge distribution, size, and hydrophobicity. Several proteins containing methylarginine modifications are fundamental to the proper regulation of DNA transcription and cell signaling. Unfortunately, PRMTs aren’t great for engineering proteins that are methylated at specific arginine sites because the enzymes rely on target sequences that a protein may not have. To get around this problem, scientists created two different methods of chemically synthesizing methylated proteins, but the involved reactions can be complicated and may require the steps to be performed manually. Therefore, it would benefit scientists to have an easier and more accurate way to make proteins with site-specific methylarginine modifications.  

In my project, I am developing a novel method of acquiring proteins with site-specific methylarginine modifications by taking advantage of the natural protein synthesis pathway rather than relying on chemical methods. Proteins are synthesized based on the combinations of three base pairs contained in a DNA transcript, called codons, which signal for another amino acid to be added to the growing chain or to stop the synthesis process. I will reassign the TAG stop codon to methylarginine and am currently designing a novel protein that can bind to and install each of the three methylarginine variants at this codon, leading to their incorporation in proteins. The novel protein, designed from the enzyme Leucyl tRNA-synthetase, will be regulated based on the concentrations of methylarginine in the cell’s environment. I will test this system in bacterial and mammalian cells to ensure it can be used to study arginine methylation in all life forms.